<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <!-- 3.外部引入 -->
    <script src="./外部.js"></script>
    <!-- 2.内嵌式 -->
    <script>
        alert('hello world!');
        alert('hello world!');
    </script>

</head>
<body>
    <!-- 1.行内式 js-->
    <input type="button" value="按钮" onclick="alert('内容')">
</body>
</html>